This invention relates to the field of networking, particularly to methods of optimizing the capacities of connections in SDH/SONET networks for packet-based traffic.
For convenience of reference, the following acronyms are used and referred to herein as follow:
The Open Systems Interconnection (OSI) model by International Organization for Standardization (ISO) is used herein as the reference for protocol layering.
Communication networks and protocols can be generally categorized into two basic types: connection oriented ones and connectionless ones. Connection oriented communication uses an established connection (such as physical circuit) between the communicating end points, and the data is (continuously) transmitted using the capacity reserved for the connection. A number of these connections, also called as channels, can be carried in a single physical wire using a technique called Time-Division Multiplexing, TDM. Connection oriented communication and TDM are commonly used for telephone traffic. The latest development in TDM technology is the Synchronous Digital Hierarchy, SDH. Somewhat simpler version of SDH used in North America is called the Synchronous Optical Network, SONET. Data communication, typically communication between computers, on the other hand, uses mainly connectionless approach. Such connectionless communication is accomplished by the transmitting the data in distinct asynchronous blocks, called packets, between the end points of communication, and such connectionless networking is thus called packet-switched. The dominating protocol in packet-switched networking currently is the Internet Protocol, IP.
It is forecasted that most of the growth in communication volumes will be in (IP-based) data traffic rather than in TDM (voice) traffic. As SDH/SONET is a connection-based (Layer 1) protocol that was mainly developed for TDM traffic and that uses operator-provisioned connections of constant bit-rate, without a method of dynamically modifying SDH/SONET connections, it is non-optimal for variable bit rate packet traffic. However, SDH/SONET is currently the dominant high-speed backbone transport network technology, and has a number of advantages including its synchronous nature, and standardized network management and traffic protection mechanisms. These advanced features of SDH/SONET equipment and networks make it more reliable data transmission technology compared to the packet-switched LAN technologies. It would also be desirable to have a common network that is efficient both for data and telecommunications.
Conventionally the connections in TDM-based networks including SDH/SONET networks are provisioned by the network operator. This makes TDM connections rather rigid and thus the trend currently is to use as few and simple (high-capacity) connections as possible to carry packet traffic between the packet switches and routers. Accordingly, conventional POS solutions use SDH/SONET connections as plain links between the adjacent switches or routers in the network, so that in conjunction with SDH/SONET ADMs that have packet-switched access interfaces there needs to be a packet switch that needs to route and process all the packet traffic from also the ring interfaces of the ADM, though typically majority of the packet traffic on backbone SDH/SONET rings are passed from one ring interface of the ADM to another. It is common that the ADMs and the packet switches required in conjunction with them are separate network elements. It is clear that this kind of network architecture is non-optimal. Particular problems are that the network throughput degrades and the delays increase in case of congestion, as a consequence of one or more of the packet switches in the network becoming overloaded. Routing traffic on packet-by-packet basis is also much more complicated and causes more delay even under normal network load than connecting packet flows as regular TDM channels between the interfaces of the network elements.
As long as TDM (SDH/SONET) connections are operator provisioned (semi-permanent), i.e. as long as there is no method for dynamically forming and adjusting the capacity of TDM (SDH/SONET) connections, the network elements that route packet traffic must perform packet switching for their entire packet traffic interface capacity to use the bandwidth efficiently. Because the units of transmission in common datacom protocols such as IP and FR are of variable size, they often need to be chopped to fixed size blocks, usually ATM cells, to facilitate line rate routing/forwarding at transport networks. ATM however is a connection-oriented (Layer 2) protocol that requires the connections to be established before traffic can be served, making it non-transparent for traffic that is not originally ATM traffic. IP for example is connectionless (Layer 3) protocol, and the networks serving IP traffic should appear as transparent for the communicating applications. Furthermore, use of ATM causes additional overhead degrading transmission efficiency and requires dedicated processing equipment and resources.
For the above reasons, there is a clear need for methods that enable more efficient, flexible and dynamic use of SDH/SONET connections for variable bandwidth data traffic. There is therefore a need for an efficient solution for carrying variable bandwidth packet traffic over simple SDH/SONET rings.
The present invention enables dynamic adjustment of the capacity of SDH/SONET connections by automatically adding and removing Paths to/from the connections formed of virtual-concatenated Paths based on the actual volumes of the packet traffic flows between the access interfaces of the SDH/SONET network and fair sharing of network resources.
The present invention provides a method to combine, without compromising, the reliability and predictability of SDH/SONET with the efficiency and flexibility of packet traffic. The packet traffic here refers to any form of digital communication where the data is transmitted in distinct asynchronous blocks (cells, frames or packets) that have a forwarding identifier with them. The method enables building of cost-efficient integrated routing and transport networks and facilitates true convergence of data communications and telecommunications.